window.onload = function(){
            var box = document.getElementById('box1');
            box.onmouseover = function(){
                run(0);
            }
            box.onmouseout = function(){
                run(-100);
            }
        }
            var timer = null;
            function run(tar){
                clearInterval(timer);
                var box = document.getElementById('box1');
                timer = setInterval(function(){
                    var speed = (tar - box.offsetLeft) / 20;
                    speed = speed > 0 ? Math.ceil(speed):Math.floor(speed);
                    if(box.offsetLeft == tar){
                        clearInterval(timer);
                    }    else    {
                        box.style.left = box.offsetLeft + speed +'px';
                    }
                },30);
            }

为什么会在left:133px处停下